Apparatus and method for vehicle emissions control

Abstract

An apparatus and method for vehicle emissions control are disclosed. More particularly, an apparatus and method for insuring that the temperature of a vehicle's exhaust gas stream entering the underfloor catalytic converter during engine operation does not exceed the temperature at which the capability of the multi-functional catalyst in the converter to absorb NO x starts to fall off. A first temperature sensor is provided in the exhaust outlet leading from the exhaust manifold of the engine and a second temperature sensor is provided in the catalytic converter. The catalytic converter contains a multi-functional catalyst such as a three-way conversion catalyst and a NO x trap as well as a NO x sensor at its outlet for sensing when NO x breakthrough is occurring. The sensors transmit their readings to a controller which transmits signal to a proportional valve located in the exhaust outlet downstream of the first temperature sensor. In response to the signals received from the controller, the proportional valve divides the exhaust gas stream received from the engine exhaust manifold into a first stream in communication with the catalytic converter and a second stream in communication with a heat exchanger. Any stream exiting the heat exchanger is then blended with the non-heat exchanged stream and the blended stream is passed into the catalytic converter. The amount of the exhaust gas stream in the first conduit will vary from that in the second conduit such that the temperature entering the catalytic converter is maintained in the range of about 300 to about 600° C. during the lean mode operation of the engine and further such that the multi-functional catalyst is periodically purged of NO x and/or SO x .

What is claimed is:  
     
       1. A method for controlling vehicle emissions which comprises: 
       (a) receiving an exhaust gas stream from the exhaust manifold of an engine through an exhaust conduit;  
       (b) providing proportional valve means in fluid communication with the exhaust conduit for dividing the gas stream into a first stream and a second stream;  
       (c) flowing at least one of the first stream into a first conduit in fluid communication with the valve means and the second stream into a second conduit in fluid communication with the valve means;  
       (d) providing a heat exchanger in fluid communication with the second conduit, said heat exchanger containing an outlet conduit in fluid communication with the first conduit downstream of the valve means;  
       (e) providing only one underfloor catalytic converter in fluid communication with the first conduit downstream of the heat exchanger outlet conduit, said catalytic converter containing a multi-functional catalyst and an outlet conduit;  
       (f) providing a first temperature sensor located in the exhaust gas conduit upstream of the valve means and a second temperature sensor located in the catalytic converter, said first and second temperature sensors having the capability of transmitting temperature readings to a controller;  
       (g) providing a NO x  sensor located in the catalytic converter outlet conduit for sensing when NO x  breakthrough is occurring;  
       (h) providing a controller in communication with the first temperature sensor, the second temperature sensor, the NO x  sensor and the valve means, said controller being capable of (1) receiving readings from the first and second sensors and the NO x  sensor and (2) transmitting signals to the valve means; and  
       (i) operating the valve means in response to the signals received from the controller to thereby divide the exhaust stream between the first conduit and the second conduit in amounts such that (1) the temperature of the exhaust gas stream flowing into the underfloor catalytic converter is maintained in the range of about 300 to about 600° C. during lean mode operation of the engine and (2) the multi-functional catalyst is periodically purged of at least one of NO x  and SO x .  
     
     
       2. The method of  claim 1  wherein: (a) the NO x  sensor senses that NO x  breakthrough is occurring and transmits a reading of the NO x  breakthrough to the controller; (b) the controller receiving such reading transmits a signal to the valve means; and (c) in response to such signal, the valve means causes the exhaust gas stream to be divided in amounts between the first conduit and the second conduit such that the temperature of the exhaust gas stream entering the underfloor catalytic converter is in the range of about 600° C. to about 750° C. such that the multi-functional catalyst is purged of SO x . 
     
     
       3. The method of  claim 1  wherein the temperature of the exhaust gas stream flowing into the underfloor catalytic converter is maintained in the range of 350 to 550° C. 
     
     
       4. The method of  claim 3  further comprising providing a close-coupled catalytic converter located upstream of the valve means. 
     
     
       5. The method of  claim 4  wherein the close-coupled catalyst unit is located immediately adjacent to the exhaust manifold. 
     
     
       6. The method of  claim 5  wherein the close-coupled catalytic converter comprises a three-way conversion catalyst. 
     
     
       7. The method of  claim 6  wherein the three-way conversion catalyst comprises one or more platinum group metals disposed on a high surface area, refractory oxide support. 
     
     
       8. The method of  claim 7  wherein the platinum group metals are selected from the group consisting of platinum, palladium, rhodium and mixtures thereof. 
     
     
       9. The method of  claim 7  wherein the support is disposed on a monolithic carrier. 
     
     
       10. The method of  claim 9  wherein the monolithic carrier comprises a refractory ceramic or metal honeycomb structure. 
     
     
       11. The method of  claim 7  wherein the support comprises gamma-alumina. 
     
     
       12. The method of  claim 11  wherein the gamma-alumina is stabilized with zirconia, titania, an alkaline earth metal oxide, one or more rare earth metal oxides and mixtures thereof. 
     
     
       13. The method of  claim 12  wherein the alkaline earth metal oxide is selected from the group consisting of baria, calcia, strontia and mixtures thereof. 
     
     
       14. The method of  claim 12  wherein the rare earth metal oxides are selected from the group consisting of ceria, lanthana and mixtures thereof. 
     
     
       15. The method of  claim 1  wherein the multi-functional catalyst comprises a three-way conversion catalyst and a NO x  trap. 
     
     
       16. The method of  claim 15  wherein the NO x  trap comprises one or more basic oxygenated compounds of one or more metals selected from the group consisting of alkali metals and alkaline earth metals. 
     
     
       17. The method of  claim 16  wherein the NO x  trap comprises one or more of basic oxygenated compounds of metals selected from the group consisting of lithium, sodium, potassium, cesium, magnesium, calcium, strontium, barium and mixtures thereof. 
     
     
       18. The method of  claim 15  wherein the three-way conversion catalyst comprises one or more platinum group metals disposed on a high surface area, refractory oxide support. 
     
     
       19. The method of  claim 18  wherein the platinum group metals are selected from the group consisting of platinum, palladium, rhodium and mixtures thereof. 
     
     
       20. The method of  claim 18  wherein the support is disposed on a monolithic carrier. 
     
     
       21. The method of  claim 20  wherein the monolithic carrier comprises a refractory ceramic or metal honeycomb structure. 
     
     
       22. The method of  claim 18  wherein the support comprises gamma-alumina. 
     
     
       23. The method of  claim 22  wherein the gamma-alumina is stabilized with zirconia, titania, an alkaline earth metal oxide, one or more rare earth metal oxides and mixtures thereof. 
     
     
       24. The method of  claim 23  wherein the alkaline earth metal oxide is selected from the group consisting of baria, calcia, strontia and mixtures thereof. 
     
     
       25. The method of  claim 23  wherein the rare earth metal oxides are selected from the group consisting of ceria, lanthana and mixtures thereof.